1. Field of the Invention
The present invention relates to a method for regenerating iridium-containing hydrocarbon conversion catalysts. More particularly, the present invention relates to a process for regenerating a supported iridium-containing hydrocarbon conversion catalyst that has been deactivated by the deposition of carbonaceous residues thereon during contact with a hydrocarbon feed stock at elevated temperature.
2. Description of the Prior Art
The deactivation of noble metal-containing hydrocarbon conversion catalysts due to the deposition on the catalyst of carbonaceous residues is as well known phenomenon. The problem with catalyst deactivation is particularly acute with respect to supported noble metal-containing catalysts employed in the hydroforming of naphtha feed stocks.
Numerous methods have been suggested by prior workers for the regeneration of supported noble metal catalysts which have been deactivated by the deposition of carbonaceous residues. In U.S. Pat. Nos. 2,916,440, 3,243,384, 3,201,355 and 3,654,182, there are disclosed procedures utilizing gaseous mixtures containing oxygen and a halogen or halogen compound, particularly hydrogen chloride, for combustion of the carbonaceous residues. Further, in U.S. Pat. No. 3,278,419 there is disclosed a procedure for the regeneration of supported platinum catalyst involving (a) addition of halogen to the catalyst while in contact with the process feed stock and (b) burning the coke deposits from the catalyst with an oxygen-containing, halogen-free regeneration gas. The prior art regeneration procedures are not completely adequate for the regeneration of iridium-containing catalysts. The performance of an iridium-containing catalyst contacted with oxygen at temperatures in excess of about 800.degree.F. before use is diminished, unless certain procedures are employed, prior to and during contact with oxygen at elevated temperature, to protect the catalyst. If such precautions are not taken, the iridium present in the catalyst will undergo oxidative agglomeration to form large iridium oxide crystallites, which revert to low surface area iridium crystallites on reduction. Further, when iridium is employed in conjunction with other metals in a multimetallic catalyst system, high temperature oxygen contacting serves to destroy the highly dispersed polymetallic clusters comprising atoms of iridium and the other metals. A separate agglomerated iridium oxide phase forms, and the activity of the catalyst is subsequently much lower.